on May 26, 2026 at 5:30 pm

The Kubernetes project relies on transparency to empower cluster administrators and security researchers. One important way we do that is by publishing CVE records into the Common Vulnerabilities and Exposures database. As part of our ongoing effort to mature the official Kubernetes CVE Feed, we have identified some discrepancies. CVE records for a few older, unfixed issues incorrectly include a fixed version field. The Kubernetes Security Response Committee (SRC) will correct the affected CVE records on June 1, 2026. This may result in vulnerability scanners identifying these vulnerabilities in places where they were previously not detected. To help reduce confusion, this post provides a technical update on three vulnerabilities that were disclosed in previous years but remain unfixed: CVE-2020-8561, CVE-2020-8562, and CVE-2021-25740. Why we are updating these records nowWhile these vulnerabilities have been public for several years, the recent work to generate official Open Source Vulnerabilities (OSV) files revealed that their corresponding CVE records did not accurately reflect their status. Specifically, some records suggested a fixed version existed, when in reality, these issues are architectural design trade-offs that cannot be fully remediated through code without breaking fundamental Kubernetes functionality. Correcting these records is vital for the community for: Automation Fidelity: Modern vulnerability scanners depend on precise version ranges. Inaccurate fixed tags lead to false negatives, giving users a false sense of security. Risk Documentation: By formalizing these as unfixed, we ensure that platform providers and administrators are aware of the persistent need for administrative mitigations. For completeness, we should also mention that CVE-2020-8554 is an unfixed CVE with a correct CVE record stating that it affects all versions. That record will also be updated to use a more-standardized version number format. Technical analysis of unfixed architectural risksThe following vulnerabilities will not be fixed by the Kubernetes project. GitHub issues remain the best reference for the technical mechanics of these flaws. CVE-2020-8561: Webhook redirect in kube-apiserver Severity: Medium (4.1). The Issue: The kube-apiserver follows HTTP redirects when communicating with admission webhooks. An actor capable of configuring an AdmissionWebhookConfiguration can redirect API server requests to internal, private networks. Why it remains unfixed: Restricting this behavior would require breaking the standard HTTP client behavior that many legitimate integrations rely on. Mitigation: Set the API server log level to less than 10 (to prevent logging response bodies) and disable dynamic profiling (–profiling=false) to prevent unauthorized log-level changes. CVE-2020-8562: Proxy bypass via DNS TOCTOU Severity: Low (3.1). The Issue: A Time-of-Check to Time-of-Use (TOCTOU) race condition in the API server proxy allows users to bypass IP restrictions. The system performs a DNS check to validate an IP, but then performs a second resolution for the actual connection, which an attacker can manipulate. Why it remains unfixed: Fixing this requires pinning resolved IPs in a way that breaks complex split-horizon DNS or dynamic IP environments. Mitigation: Use a local DNS caching server like dnsmasq for the API server and configure min-cache-ttl to enforce consistent responses between the check and the connection. CVE-2021-25740: Cross-namespace forwarding via Endpoints Severity: Low (3.1). The Issue: A design flaw in the Endpoints and EndpointSlice API objects allows users to manually specify IP addresses, which can be used to point a LoadBalancer or Ingress toward backends in other namespaces. Why it remains unfixed: This is a fundamental feature of the Endpoints API used by many networking tools and operators. Mitigation: Restrict write access to Endpoints (legacy) and EndpointSlices. Since Kubernetes 1.22, Kubernetes RBAC authorization mode no longer includes those permissions in the default edit and admin ClusterRoles. That removal applies to clusters created using Kubernetes v1.22; for clusters upgraded from older versions, administrators should manually audit and reconcile the system:aggregate-to-edit ClusterRole. Note:On June 1, 2026, these CVE records will be updated to correctly reflect the fact that all versions are affected. You may see them begin to appear in vulnerability scanner results. Required actions for administratorsThe Kubernetes project recommends a secure by configuration approach to manage these persistent risks: Vulnerability Action item Severity score (Rating) Command / configuration CVE-2020-8561 Restrict Log Verbosity 4.1 (Medium) Ensure –v is set to < 10 and –profiling=false. CVE-2020-8562 Enforce DNS Consistency 3.1 (Low) Deploy dnsmasq or a similar caching resolver on control plane nodes. CVE-2021-25740 Hardened RBAC 3.1 (Low) kubectl auth reconcile to remove Endpoints write access from broad roles. The RBAC action for CVE-2021-25740 applies when your cluster uses RBAC authorization mode, which is the default for clusters created with standard Kubernetes tooling. Administrators should independently test and validate these configurations in a non-production environment, assessing the architectural risks against their specific threat model and risk tolerance. Conclusion: maturity through transparencyThe effort to reconcile these records is a sign of a maturing security ecosystem. By moving away from the “patch-only” mindset and accurately documenting architectural debt, the Kubernetes project provides the community with the high-fidelity data needed to secure modern cloud native infrastructure. We would like to thank the security researchers—QiQi Xu, Javier Provecho, and others—who identified these risks, and the SIG Security Tooling contributors who continue to refine our official feeds. Special shoutout to Rory McCune for sharing information around these CVEs through his blog posts.

on May 20, 2026 at 12:00 am

SIG-Etcd announces the availability of the first beta release of etcd v3.7.0. This new version of the popular distributed database and key Kubernetes component includes the long-requested RangeStream feature, as well as a refactoring and cleanup of multiple legacy components and interfaces. v3.7 will deliver improved security, better operational reliability, and an improved experience for working with large resultsets. First, however, the project needs users to test the beta. You can find v3.7.0-beta.0 here: Source code Binaries Official container images Please try it out and report issues in the etcd repo. This beta also determines the EOL of version 3.4. RangeStreamIn etcd v3.6 and earlier, it is challenging to work with requests that return large resultsets. The client or requesting application is forced to wait for the full result set, leading to unpredictable latency and memory usage. The RangeStream RPC lets calling applications accept result sets in chunks, reducing latency and making buffering memory usage more predictable. Much of the work on RangeStream was done by a relatively new contributor to etcd, Jeffrey Ying, a software engineer at Google. New contributors can have a substantial impact on etcd development. “I’ve always been fascinated by database internals, and building RangeStream was a great opportunity to solve a bottleneck we were hitting in production with Kubernetes. It was the perfect opportunity to collaborate across projects and improve the ecosystem as a whole. Jumping into etcd as a new contributor had a bit of a learning curve, but the community is incredibly welcoming. The leads were very receptive to my ideas and helped me iterate quickly, while maintaining the project’s high bar for reliability and code quality,” said Jeffrey. Instructions on how to use RangeStream in gRPC calls and in etcdctl can be found in the etcd documentation. Users should try it out for their own applications. Removal of v2storeThe last vestiges of etcd v2store have been removed in v3.7, making this the first release that is 100% on v3store. This includes discovery, bootstrap, v2 requests, and the v2 client. Our team has also removed multiple deprecated experimental flags. All of these changes may create some breakage for users, particularly those who have not already updated to v3.6.11. We are interested in hearing about blockers encountered by users and dependent applications; please report anything you find that can’t be remedied or needs better upgrade documentation. etcd v3.7.0-beta.0 also includes bbolt v1.5.0 and raft v3.7.0. 3.4 EOLAccording to our community support policy, we typically maintain only the latest two minor versions, currently v3.6 and v3.5. Etcd v3.5 will be supported for 1 year after v3.7.0 final release. As mentioned in extended support for v3.4 in the etcd v3.6.0 release announcement, etcd v3.4 has been EOL since May 15, 2026. SIG-etcd may release one more security patch for that version at the end of May, if warranted by patched vulnerabilities. In any case, it will cease being updated after the end of May. Users on v3.4 should be planning to upgrade their clusters. Feedback and Future BetasReach the etcd contributors with your feedback about v3.7.0-beta.0 in any of the following places: Github issues #SIG-etcd slack channel in Kubernetes Slack etcd-dev mailing list SIG-etcd may release additional betas of version v3.7.0 with additional refactoring, particularly of our use of protobuf libraries. Release candidates and the final release will probably happen through June, possibly into early July.

on May 15, 2026 at 6:35 pm

This article was originally published with the wrong date. It was later republished, dated the 15th of May 2026. Kubernetes v1.36 introduces a new alpha counter metric route_controller_route_sync_total to the Cloud Controller Manager (CCM) route controller implementation at k8s.io/cloud-provider. This metric increments each time routes are synced with the cloud provider. A/B testing watch-based route reconciliationThis metric was added to help operators validate the CloudControllerManagerWatchBasedRoutesReconciliation feature gate introduced in Kubernetes v1.35. That feature gate switches the route controller from a fixed-interval loop to a watch-based approach that only reconciles when nodes actually change. This reduces unnecessary API calls to the infrastructure provider, lowering pressure on rate-limited APIs and allowing operators to make more efficient use of their available quota. To A/B test this, compare route_controller_route_sync_total with the feature gate disabled (default) versus enabled. In clusters where node changes are infrequent, you should see a significant drop in the sync rate with the feature gate turned on. Example: expected behaviorWith the feature gate disabled (the default fixed-interval loop), the counter increments steadily regardless of whether any node changes occurred: # After 10 minutes with no node changes route_controller_route_sync_total 60 # After 20 minutes, still no node changes route_controller_route_sync_total 120 With the feature gate enabled (watch-based reconciliation), the counter only increments when nodes are actually added, removed, or updated: # After 10 minutes with no node changes route_controller_route_sync_total 1 # After 20 minutes, still no node changes — counter unchanged route_controller_route_sync_total 1 # A new node joins the cluster — counter increments route_controller_route_sync_total 2 The difference is especially visible in stable clusters where nodes rarely change. Where can I give feedback?If you have feedback, feel free to reach out through any of the following channels: The #sig-cloud-provider channel on Kubernetes Slack The KEP-5237 issue on GitHub The SIG Cloud Provider community page for other communication channels How can I learn more?For more details, refer to KEP-5237.

on May 15, 2026 at 6:00 pm

Back in Kubernetes 1.28, we introduced the Mixed Version Proxy (MVP) as an Alpha feature (under the feature gate UnknownVersionInteroperabilityProxy) in a previous blog post. The goal was simple but critical: make cluster upgrades safer by ensuring that requests for resources not yet known to an older API server are correctly routed to a newer peer API server, instead of returning an incorrect 404 Not Found. We are excited to announce that the Mixed Version Proxy is moving to Beta in Kubernetes 1.36 and will be enabled by default! The feature has evolved significantly since its initial release, addressing key gaps and modernizing its architecture. Here is a look at how the feature has evolved and what you need to know to leverage it in your clusters. What problem are we solving?In a highly available control plane undergoing an upgrade, you often have API servers running different versions. These servers might serve different sets of APIs (Groups, Versions, Resources). Without MVP, if a client request lands on an API server that does not serve the requested resource (e.g., a new API version introduced in the upgrade), that server returns a 404 Not Found. This is technically incorrect because the resource is available in the cluster, just not on that specific server. This can lead to serious side effects, such as mistaken garbage collection or blocked namespace deletions. MVP solves this by proxying the request to a peer API server that can serve it. sequenceDiagram participant Client participant API_Server_A as API Server A (Older/Different) participant API_Server_B as API Server B (Newer/Capable) Client->>API_Server_A: 1. Request for Resource (e.g., v2) Note over API_Server_A: Determines it cannot serve locally API_Server_A->>API_Server_A: 2. Looks up capable peer in Discovery Cache API_Server_A->>API_Server_B: 3. Proxies request (adds x-kubernetes-peer-proxied header) API_Server_B->>API_Server_B: 4. Processes request locally API_Server_B–>>API_Server_A: 5. Returns Response API_Server_A–>>Client: 6. Forwards Response How has it evolved since 1.28The initial Alpha implementation was a great proof of concept, but it had some limitations and relied on older mechanisms. Here is how we have modernized it for Beta: From StorageVersion API to Aggregated Discovery In the Alpha version, API servers relied on the StorageVersion API to figure out which peers served which resources. While functional, this approach had a significant limitation: the StorageVersion API is not yet supported for CRDs and aggregated APIs. For Beta, we have replaced the reliance on StorageVersion API calls with the use of Aggregated Discovery. API servers now use the aggregated discovery data to dynamically understand the capabilities of their peers. The Missing Piece: Peer-Aggregated Discovery The 1.28 blog post noted a significant gap: while we could proxy resource requests, discovery requests still only showed what the local API server knew about. In 1.36, we have added Peer-Aggregated Discovery support! Now, when a client performs discovery (e.g., listing available APIs), the API server merges its local view with the discovery data from all active peers. This provides clients with a complete, unified view of all APIs available across the entire cluster, regardless of which API server they connected to. sequenceDiagram participant Client participant API_Server_A as API Server A participant API_Server_B as API Server B Client->>API_Server_A: 1. Request Discovery Document API_Server_A->>API_Server_A: 2. Gets Local APIs API_Server_A->>API_Server_B: 3. Gets Peer APIs (Cached or Direct) API_Server_A->>API_Server_A: 4. Merges and sorts lists deterministically API_Server_A–>>Client: 5. Returns Unified Discovery Document While peer-aggregated discovery will be the default behavior (note that peer-aggregated discovery is enabled if the –peer-ca-file flag is set, otherwise the server will fallback to showing only its local APIs), there may be cases where you need to inspect only the resources served by the specific API server you are connected to. You can request this non-aggregated view by including the profile=nopeer parameter in your request’s Accept header (e.g., Accept: application/json;g=apidiscovery.k8s.io;v=v2;as=APIGroupDiscoveryList;profile=nopeer). Required configurationWhile the feature gate will be enabled by default, it requires certain flags to be set to allow for secure communication between peer API servers. To function correctly, make sure your API server is configured with the following flags: –feature-gates=UnknownVersionInteroperabilityProxy=true: This will be default in 1.36, but it is good to verify –peer-ca-file=<path-to-ca>: [CRITICAL] This is a required flag. You must provide the CA bundle that the source API server will use to authenticate the serving certificates of destination peer API servers. Without this, proxying will fail due to TLS verification errors. –peer-advertise-ip and –peer-advertise-port: These flags are used to set the network address that peers should use to reach this API server. If unset, the values from –advertise-address or –bind-address are used. If you have complex network topologies where API servers communicate over a specific internal interface, setting these flags explicitly is highly recommended. Configuring with kubeadmIf you manage your cluster with kubeadm, you can configure these flags in your ClusterConfiguration file: apiVersion: kubeadm.k8s.io/v1beta4 kind: ClusterConfiguration apiServer: extraArgs: peer-ca-file: “/etc/kubernetes/pki/ca.crt” # peer-advertise-ip and port if needed Call to actionIf you are running multi-master clusters and upgrading them regularly, the Mixed Version Proxy is a major safety improvement. With it becoming default in 1.36, we encourage you to: Review your API server flags to ensure –peer-ca-file is set properly. Test the feature in your staging environments as you prepare for the 1.36 upgrade. Provide feedback to SIG API Machinery (Slack, mailing list, or by attending SIG API Machinery meetings) on your experience.

on May 14, 2026 at 6:35 pm

The .spec.externalIPs field for Service was an early attempt to provide cloud-load-balancer-like functionality for non-cloud clusters. Unfortunately, the API assumes that every user in the cluster is fully trusted, and in any situation where that is not the case, it enables various security exploits, as described in CVE-2020-8554. Since Kubernetes 1.21, the Kubernetes project has recommended that all users disable .spec.externalIPs. To make that easier, Kubernetes also added an admission controller (DenyServiceExternalIPs) that can be enabled to do this. At the time, SIG Network felt that blocking the functionality by default was too large a breaking change to consider. However, the security problems are still there, and as a project we’re increasingly unhappy with the “insecure by default” state of the feature. Additionally, there are now several better alternatives for non-cloud clusters wanting load-balancer-like functionality. As a result, the .spec.externalIPs field for Service is now formally deprecated in Kubernetes 1.36. We expect that a future minor release of Kubernetes will drop implementation of the behavior from kube-proxy, and will update the Kubernetes conformance criteria to require that conforming implementations do not provide support. A note on terminology, and what hasn’t been deprecatedThe phrase external IP is somewhat overloaded in Kubernetes: The Service API has a field .spec.externalIPs that can be used to add additional IP addresses that a Service will respond on. The Node API’s .status.addresses field can list addresses of several different types, one of which is called ExternalIP. The kubectl tool, when displaying information about a Service of type LoadBalancer in the default output format, will show the load balancer IP address under the column heading EXTERNAL-IP. This deprecation is about the first of those. If you are not setting the field externalIPs in any of your Services, then it does not apply to you. That said, as a precaution, you may still want to enable the DenyServiceExternalIPs admission controller to block any future use of the externalIPs field. Alternatives to externalIPsIf you are using .spec.externalIPs, then there are several alternatives. Consider a Service like the following: apiVersion: v1 kind: Service metadata: name: my-example-service spec: type: ClusterIP selector: app.kubernetes.io/name: my-example-app ports: – protocol: TCP port: 80 targetPort: 8080 externalIPs: – “192.0.2.4” Using manually-managed LoadBalancer Services instead of externalIPsThe easiest (but also worst) option is to just switch from using externalIPs to using a type: LoadBalancer service, and assigning a load balancer IP by hand. This is, essentially, exactly the same as externalIPs, with one important difference: the load balancer IP is part of the Service’s .status, not its .spec, and in a cluster with RBAC enabled, it can’t be edited by ordinary users by default. Thus, this replacement for externalIPs would only be available to users who were given permission by the admins (although those users would then be fully empowered to replicate CVE-2020-8554; there would still not be any further checks to ensure that one user wasn’t stealing another user’s IPs, etc.) Because of the way that .status works in Kubernetes, you must create the Service without a load balancer IP, and then add the IP as a second step: $ cat loadbalancer-service.yaml apiVersion: v1 kind: Service metadata: name: my-example-service spec: # prevent any real load balancer controllers from managing this service # by using a non-existent loadBalancerClass loadBalancerClass: non-existent-class type: LoadBalancer selector: app.kubernetes.io/name: my-example-app ports: – protocol: TCP port: 80 targetPort: 8080 $ kubectl apply -f loadbalancer-service.yaml service/my-example-service created $ kubectl patch service my-example-service –subresource=status –type=merge -p ‘{“status”:{“loadBalancer”:{“ingress”:[{“ip”:”192.0.2.4″}]}}}’ Using a non-cloud based load balancer controllerAlthough LoadBalancer services were originally designed to be backed by cloud load balancers, Kubernetes can also support them on non-cloud platforms by using a third-party load balancer controller such as MetalLB. This solves the security problems associated with externalIPs because the administrator can configure what ranges of IP addresses the controller will assign to services, and the controller will ensure that two services can’t both use the same IP. So, for example, after installing and configuring MetalLB, a cluster administrator could configure a pool of IP addresses for use in the cluster: apiVersion: metallb.io/v1beta1 kind: IPAddressPool metadata: name: production namespace: metallb-system spec: addresses: – 192.0.2.0/24 autoAssign: true avoidBuggyIPs: false After which a user can create a type: LoadBalancer Service and MetalLB will handle the assignment of the IP address. MetalLB even supports the deprecated loadBalancerIP field in Service, so the end user can request a specific IP (assuming it is available) for backward-compatibility with the externalIPs approach, rather than being assigned one at random: apiVersion: v1 kind: Service metadata: name: my-example-service spec: type: LoadBalancer selector: app.kubernetes.io/name: my-example-app ports: – protocol: TCP port: 80 targetPort: 8080 loadBalancerIP: “192.0.2.4” Similar approaches would work with other load balancer controllers. This approach can allow cluster administrators to have control over which IP addresses are assigned, rather than users. Using Gateway APIAnother potential solution is to use an implementation of the Gateway API. Gateway API allows cluster administrators to define a Gateway resource, which can have an IP address attached to it via the .spec.addresses field. Since Gateway resources are designed to be managed by cluster administrators, RBAC rules can be put in place to only allow privileged users to manage them. An example of how this could look is: apiVersion: gateway.networking.k8s.io/v1 kind: Gateway metadata: name: example-gateway spec: gatewayClassName: example-gateway-class addresses: – type: IPAddress value: “192.0.2.4” — apiVersion: gateway.networking.k8s.io/v1 kind: HTTPRoute metadata: name: example-route spec: parentRefs: – name: example-gateway rules: – backendRefs: – name: example-svc port: 80 — apiVersion: v1 kind: Service metadata: name: example-svc spec: type: ClusterIP selector: app.kubernetes.io/name: example-app ports: – protocol: TCP port: 80 targetPort: 8080 The Gateway API project is the next generation of Kubernetes Ingress, Load Balancing, and Service Mesh APIs within Kubernetes. Gateway API was designed to fix the shortcomings of the Service and Ingress resource, making it a very reliable robust solution that is under active development. Timeline for externalIPs deprecationThe rough timeline for this deprecation is as follows: With the release of Kubernetes 1.36, the field was deprecated; Kubernetes now emits warnings when a user uses this field About a year later (v1.40 at the earliest) support for .spec.externalIPs will be disabled in kube-proxy, but users will have a way to opt back in should they require more time to migrate away About another year later – (v1.43 at the earliest) support will be disabled completely; users won’t have a way to opt back in